1. Field of the Invention
The invention relates to the field of building panels, in particular precast wall or facing panels of the type made by setting stones in an array and casting concrete around only a rear part of the stones. The concrete bonds to the stones, leaving front or outer sides of the stones exposed between gaps resembling mortar joints. When the panel is erected, the resulting wall or facing has the appearance of a masonry wall that was assembled stone by stone using mortar. The invention additionally concerns the formation of corners in such structures and further provides means by which embedded coil threaded structures that support reinforcing rods during casting are used for mounting the panels to one another or to other structures.
2. Prior Art
It is known to precast individual panels and to mount them to a structure, or to abut the panels edgewise to form a wall, a facing for a wall, a paving element or a similar structure, using the panels as modular building elements. Such panels are cast in a shallow horizontal mold and can be installed horizontally, vertically or otherwise as appropriate. According to one concrete casting technique for making panels, a number of stones, bricks, blocks or the like are set in an array in a frame-like mold containing a loose material such as sand or a removable material such as wax, leaving spaces between the stones occupied by the removable material. Concrete is poured over the stones and allowed to cure, bonding to the inner or rear faces of the stones and to the sides of the stones along the spaces. The idea is that the sand or other loose or removable material will keep the poured concrete from reaching the front or outer faces of the stones, blocks or the like, so that the faces will be exposed after the concrete has cured and the panel is lifted out of the mold, and cleaned of the removable material. This technique is applicable to various stone and block materials and various different shapes, all such stones, blocks and the like being termed simply "stones" in this disclosure.
Typically, a bed of sand is placed in the mold and the surface of the sand is levelled to provide a uniform depth. The stones are laid vertically upon and pushed downwardly into the bed of sand. Sand also can be poured or brushed into the spaces between the stones, instead of or in addition to using an initial levelled bed of sand. The sand or other removable material is placed to the required depth to control the extent to which the stones or blocks protrude from the finished casting. Whereas the stones or blocks are slightly spaced from one another and protrude from the concrete in the finished product, the panel resembles a masonry structure in which the stones or blocks were assembled using mortar joints.
Casting various types of panels using various types of stones or blocks in the foregoing manner is disclosed, for example, in U.S. Pat. Nos. 1,169,985--Mickelson; 1,916,308--Grieco; 2,151,420--Carvel; 3,390,496--Weiner et al.; and, 3,874,140--Seehusen. In U.S. Pat. No. 2,047,648--Pollard, such a block is cast vertically using straw or dried mud as the material for keeping the concrete from flowing onto the outer faces of the embedded stones. Additional related disclosures are found in U.S. Pat. Nos. 1,838,203--Wales; 2,149,784--McClatchy et al.; 2,151,420--Carvel; 3,331,175--Terrio; 3,646,715--Pope; 4,219,984--de San; German Patent 2,839,704--Sickau; British Patent 732,431--Davie et al.; and Italian Patents 356,516 and 551,154.
Although forming a precast simulation of an assembled masonry wall as described appears to be a straightforward operation, problems are encountered in practice. A primary problem is that when pouring concrete over the array of stones in the sand bed, it is difficult to prevent the concrete from flowing through the removable material and/or around the stones to the front face of the stones, where the intruding concrete ruins the effect. Part of the problem is the tendency of the thick and heavy poured concrete aggregate to displace either or both of the sand in the sand bed and the stones set therein. Displacement of the sand and stones opens flow paths, resulting in intrusions of the concrete into isolated areas between and on the front faces of the stones. Another aspect is that the sand mixes with the concrete and becomes part of the concrete aggregate. If the concrete is allowed to set when wholly or partly covering the front face of one or more stones, either it must be chipped or cleaned away, or the cast panel will be unsightly and wasted. Normally the sand adhering to the concrete provides a particular colored appearance (e.g., tan). If the concrete intrudes into the spaces between the stones, by displacing the sand, the distinct color of the intruding concrete (e.g., gray) is likewise noticeable and unsightly.
A less easily displaced material such as liquid wax or mud can be used instead of sand and allowed to harden before casting the concrete, but such materials are inconvenient. Any misplaced material applied to the rear part of the stones interferes with bonding between the stones and the concrete. Cleanup after casting is a problem for these less-easily displaced materials. Even using sand, efforts may be required to remove sand or sand/cement aggregate between the stones, or to dress up the appearance of the panel by pointing or the like.
In the conventional technique, a bed of sand deeper than the desired distance by which the stones are to protrude, is first placed in the mold. The stones are laid on the sand bed. The stones depress the sand underneath the stones, but sand remains under each stone, the stones "floating" on the sand bed. Natural stone usually is be at least somewhat rounded or tapered toward the edges, with the result that the sand under the middle of each stone is most compressed (but remains between the stone and the bottom of the casting mold); the sand spaced from the middle is less compressed; and the sand in spaces between the stones is not compressed at all. Thus the stones and sand are not stable nor are they evenly packed.
It is possible to add sand to the spaces between the stones after the stones are in place, for example by pouring additional sand over the laid stones and brushing the sand off the rear faces of the stones and into the spaces between the stones. However, it is difficult or impossible adequately to pack the sand between and under the rounded parts of the stones, which areas are inaccessible due to the presence of the stones and their rounded shape. In fact compressing the sand by simply laying the stones on a sand bed tends to form a pedestal of compressed sand under the center of the stone and uncompressed sand around its perimeter, which is unstable. This is not remedied simply by wiggling the stone when placing it, because sand remains under the stone. Wiggling stones when placing them also disturbs adjacent stones and sand, as well as causing uneven inter-stone spacing that is inconsistent with the traditional masonry appearance, wherein great effort is expended to space the stones evenly.
Another problem is how to resolve the presence of the stones, sand and concrete with the structural needs and practical problems encountered in building using precast panels generally. These problems include providing good structural strength and appropriate means for handling the panels when cured. A cast panel may weigh on the order of 2,000 to 3,000 lbs. (900-1,400 kg).
Other problems include how to join coplanar panels in endwise abutting relationships without extremely apparent seams and/or how to mount the panels, for example facewise to a surface such as a vertical wall or to enclose a column. Advantageously, the panels should be adaptable to various different types and shapes of structures that are advantageously faced with stone.
Another problem is how to form corners, particularly since the rear face of the panel is concrete and the edge of at least one of the two panels at a corner normally will be visible when two panels are abutted, for example at 90.degree.. Visible edges and seams detract from the objective of simulating an assembled masonry wall. Seams and edges are a problem at corners and where panels are needed to face around polygonal shapes such as corner posts, monuments or chimneys, due to the layered structure of the panels. The layered planar structure is inconsistent with forming corners and three dimensional forms such as three panel channels (e.g., to face a chimney), boxes and non-rectilinear forms.
It would be advantageous if these matters could be resolved in a reinforced panel that can be constructed in a convenient and effective manner.